This invention relates generally to large screen projection lenses for television receiver and monitor displays and particularly to large screen projection lenses that are made up of two separate elements, such as a fresnel lens and a lenticular lens.
It is common practice with large screen projection systems to include a plastic lens system consisting of a planar fresnel lens and a planar lenticular lens that are supported in full surface contact with each other. Difficulties often arise due to temperature changes, mechanical problems and the like where one of the lens elements departs from its flat configuration and separates from the other lens element. This can result in local screen imperfections such as distortion, defocusing and color impurities, all of which are very disturbing to a viewer. With the present invention, a similar curve is imparted to both of the lens elements and consequently, they tend to stay together during temperature cycling and despite minor mechanical imperfections in the lens elements and their supporting structure. Hence a more reliable large screen projection lens is produced with the invention.
The curve that is imparted may be cylindrical, spherical parabolic, etc., depending upon the design environment. Should correction of the images be required as a result of the curved screen configuration, well-known waveform correction circuitry may be employed for this purpose. It is also anticipated that the type of screen curve configuration used may alleviate the display geometry problems in the receiver and lead to simpler implementations.
In addition to the curved configuration of the lens elements, the invention includes a novel mounting arrangement for the lens. Essentially, a flexible strip having a T-shaped cross section is used in conjunction with a groove in a frame or housing of matching contour for securing the two lens elements in position. The mounting arrangement is simple and effective and the leg of the T-shaped flexible strip also serves to provide a covering for the edges of the two lens elements.